Cyanides are used in a variety of industrial applications, such as in the art of electroplating, steel heat treating and mining. In these processes, however, the waste solutions contain cyanide which presents a significant environmental hazard. Strict governmental regulations are in place which control the release of cyanides. This has necessitated the development of various processes to remove cyanides from waste waters. One example of treating cyanides is by alkaline chlorination. Chlorine and sodium hydroxide may be used to oxidize the cyanide to cyanates and subsequently to carbon dioxide and water. The problem with the alkaline chlorination process is that:
(1) chemical consumption increases with cyanide content in the waste waters; hence significantly increasing operating costs; PA1 (2) the process does not destroy iron and other complex cyanides and hence dilution must be relied upon to comply with regulations; PA1 (3) very careful control of the reaction is required; otherwise toxic cyanogen chloride can be released.
Another technique for removing cyanide from waste waters is by way of hydrolysis. At high temperatures and pressures, the following reaction proceeds rather quickly: EQU CN.sup.- +2 H.sub.2 O.fwdarw.HCOO.sup.- +NH.sub.3
An example of such hydrolysis is disclosed in U.S. Pat. No. 4,042,502. This patent discloses the use of a heat exchanger which has first and second flow paths where the second flow path is in heat exchange contact with fresh cyanide solution which is introduced to the heat exchanger through the first flow path. For the system to function, there is a continuous effluent flow to ensure constant heat exchange with continuous inflow of waste waters to be treated. Preferably, laminar flow is maintained within the heat exchanger which also constitutes the reactor. By way of heating the incoming waste waters in a preheater to a temperature of more than half the temperature reached in the heat exchange reactor, the system provides for continuous reaction within the heat exchanger. However, it is appreciated that with cyanide hydrolysis reactions, solids are generated as the cyanides are destroyed creating a build-up of sludge which presents a significant problem in having the reaction carried out within the heat exchanger due to flow of the effluent through valves and the like in which sludge can build up and detract from the overall efficiency of the hydrolysis reaction in the heat exchanger.